Method and apparatus for impregnating stranded wires during stranding thereof

ABSTRACT

Method and apparatus for filling and coating the strands of a fully-filled electric cable. The wires, or groups of wires, are passed through a tank containing the filling and coating material in a liquid state and at a temperature above its dropping point temperature while the wires are being stranded together in the tank and as the so-stranded and filled wires leave the tank they are subjected to cooling, causing the material to solidify, and the material is smoothed and reduced to the desired size. The tank has a perforated guiding plate at its input, the wires, or groups of wires, passing through the perforations and the tank contains one or more dies through which the stranded wires or groups pass. The tank is temperature regulated and provision is made for recirculation of overflow or leaked filling material. The cooling and smoothing is accomplished in a tube at the exit of the tank which tube is surrounded by a cooling fluid.

United States Patent [191 Portinari et al.

[ METHOD AND APPARATUS FOR IMPREGNATING STRANDED WIRES DURING STRANDING THEREOF [75] Inventors: Antonio Portinari, Sesto San Giovanni; Giovanni Alimenti, Milan,

both of Italy [73] Assignee: Industrie Pirelli Societa per Azioni,

Milan, Italy [22] Filed: July 24, 1973 [21] Appl. N0.: 382,274

[30] Foreign Application Priority Data Aug. 2, 1972 Italy 27778/72 [52] US. Cl 57/7; 57/164 [51] Int. Cl.... B65h 81/08; I-IOlb 3/42; I-IOlb 13/24 [58] Field of Search 57/3, 6, 7, 35, 156, 160,

[56] References Cited UNITED STATES PATENTS 2,94l,348 6/1960 Biche et al 57/7 3,425,207 2/1969 Campbell 3,443,374 5/l969 Carnevale 57/162 X June 17, 1975 8/1971 Wardley ..57/7 3/1972 Lang 57/162X Delahunty [5 7 ABSTRACT Method and apparatus for filling and coating the strands of a fully-filled electric cable. The wires, or groups of wires, are passed through a tank containing the filling and coating material in a liquid state and at a temperature above its dropping point temperature while the wires are being stranded together in the tank and as the so-stranded and filled wires leave the tank they are subjected to cooling, causing the material to solidify, and the material is smoothed and reduced to the desired size. The tank has a perforated guiding plate at its input, the wires, or groups of wires, passing through the perforations and the tank contains one or more dies through which the stranded wires or groups pass. The tank is temperature regulated and provision is made for recirculation'of overflow or leaked filling material. The cooling and smoothing is accomplished in a tube at the exit of the tank which tube is surrounded by a cooling fluid.

7 Claims, 3 Drawing Figures rue: Fear/4,9750 75 SHEET PATENTEDJUN 1 7 I975 L Ll 1 METHOD AND APPARATUS FOR IMPREGNATING STRANDED WIRES DURING STRANDING THEREOF The present invention relates to the manufacture of electric cables, in particular, telecommunication cables of the type comprising a strand of several conductive elements, individually insulated, enclosed in an impermeable sheath and provided with a water-impermeable medium in the spaces existing in the strand and between it and the sheath. Cables of this kind are commonly known as fully-filled cables" and will be designated by this expression in the present specification.

One type of fully-filled cable comprises a strand of several conductive elements insulated with plastic material, for example, polyethylene. The strand is the bundle obtained by bringing together single conductors appropriately insulated, or the pairs, quads, trefoils, etc. constituted by stranding individually insulated wires. In the practice, two types of strands can be provided. One of them is called concentric," because it is formed by several layers of conductive elements arranged concentrically, one layer on the other, about the axis of the strand, while the other is called unit type strand, being formed by stranding bundles of conductive elements. Said bundles, in turn, can be formed concentrically or in groups.

The spaces existing inside the strand and between it and the sheath usually are filled with a waterimpermeable medium, mainly intended to prevent water infiltration along the cable and inside the sheath, in the event of rupture of the latter. The filling medium is such that, at normal temperatures, it does not tend to migrate along the cable and at the same time permits the necessary relative sliding movements of the conductors, required by the bending which takes place during the cable manufacture and installation.

In practice, said filling material is constituted by substances which are semi-solid at room temperature which, because of their non-homogeneous nature, do not have a melting point at a definite temperature value, but change their physical state within a limited temperature range, in general, a range of about passing gradually from the semi-solid to the liquid state. As is known, reference is made in describing said substances to the so-called dropping point, which indicates the temperature at which the substance in question, during theheating treatment, begins to soften, giving rise to drops. Said dropping point is determined by the American Society of Testing Materials, Test D 566-42. The substances which are used as a filling medium usually consist of microcrystalline petroleum waxes, mixtures of said waxes with oils, usually called petroleum jelly,, or of olefine polymers of low molecular weight.

In the process for manufacturing fully-filled cables, the step of filling the cable strand with the filling medium represents the most critical phase, since it must be ensured that said filling medium fills as completely as possible all the empty spaces existing between the conductive elements.

Various conventional techniques are used for carrying out said filling operation. Such techniques comprise 2 on the principle of injecting the filling medium in liquid or semi-solid state during the step of formation of each concentric layer of the strand itself. The filling techniques carried out on the already formed strand are, instead, grounded on the principle of injecting in said strand the filling medium in a liquid state by application of pressure and/or by preliminary "creation of vacuum.

The hereinbefore mentioned techniques, which are satisfactory under many conditions, have, however, some disadvantages. Those used for filling the strand in the stranding phase require, in general, a complicated apparatus comprising several injection devices, independent of one another and in a number corresponding to the number of layers of the strand. Moreover, they are unsuitable for strands to be formed in groups.

The methods for filling the already formed strand can be applied to strands of any type, irrespective of their formation, provided that they are constituted by a relatively small number of elements, in order to permit the filling medium to fill the strand completely. Moreover, this technique is followed only when the substance chosen as the filling medium can be applied at such a temperature as not to become solidified once it has come into contact with-the strand and, consequently, not to originate an irregular filling of the spaces inside the strand, said temperature being, in any event, such as not to cause damage'to the elements of the strand.

The present invention has, as its principal object, the providing of a complete filling of the strand of a cable of the type described hereinbefore, with a filling medium, whatever the structure of the strand may 'be, without the hereinbefore mentioned disadvantages and without employing particularly complicated equipment or processing steps.

Accordingly, one object of the present invention is a process for manufacturing a fully-filled electric cable which comprises the step of producing-a stranded assembly by starting with components of elongated shape and indefinite length and simultaneously providing said stranded assembly with a water-impermeable and electrically insulating filling medium. Saidprocess is characterized by the fact that the stranding of said components to form said assembly is carried out continuously along a substantially longitudinal path, and said components are immersed, during the stranding step, in the filling medium maintained at a temperature higher by at least 5C than its dropping point temperature, the stranded assembly subsequently being brought to a temperature lower by at least 5C than the dropping point temperature of said filling medium and the layer of filling medium impregnating said assembly being simultaneously smoothed and reduced to the desired size. I

In the present specification, the expression producing a stranded assembly by starting from components of elongated shape and indefinite length is intended to refer to any of the various stranding steps of a known process for the manufacture of a cable. Therefore, the stranded assembly can be, for example, thefinal strand, or a group which will be used to form said strand, or a subgroup, etc. Correspondingly, the components can be, for example, groups of sub-groups, of trefoils, quads, pairs, individual wires, etc.

In any case, the essence of the invention lies in the fact that the components which are to be stranded together are immersed in the liquid filling 'medium before, during and after they are stranded, so that a substantially perfect impregnation is obtained.

The components can reach the stranding station already impregnated (in an analogous preceding step or according to another impregnation method) or not impregnated. In the latter case, it is advisable for the components to comprise a relatively small number of wires inorder that the immersion preceding their stranding will be sufficient to impregnate them.

Irrespective of the structure of the components, their stranding is effected during the time that they are immersed in the filling medium by either a rotating paying-off or a rotating collecting system, of a type known in the art.

Afurther object of the present invention is to provide apparatus suitable for carrying out the hereinbefore described process. Said apparatus comprises: a. at least a temperature regulated tank containing a filling medium at a temperature higher by at least C than the dropping point temperature of said filling medium, said tank being provided, at least at one of its walls and below the level of said filling medium, with a plate able, if necessary, to rotate about its own axis and having through holes arranged around said axis, each of said holes being intended for the passage of one component and said tank being. also provided, at the opposite wall, with a hole having a diameter corresponding approximately to that of the assembly formed by said components stranded in said tank;

b. at least a die for bringing said components together and situated inside said tank and fully immersed in the filling medium, said die also being the stranding place for said components; and

c. a tube connected at one end with said hole in the wall of said tank, and provided with conventional means to maintain it at a temperature lower by at least 5C than the dropping point temperature of said filling medium, the other end of said tube being free and said tube having a diameter preferably not exceeding the diameter of the stranded assembly passing through it by more than 2 millimeters, providing, in this way, a means for smoothing and sizing the layer of the filling medium impregnating said assembly.

The process steps for producing a stranded assembly and for providing it simultaneously with the filling medium to obtain a telecommunication cable of the fullyfilled type according to the present invention, and the related apparatus will be more clearly understood from the following detailed description of preferred embodiments thereof, which description should be considered in conjunction with the accompanying drawings in which: 7

FIG. 1 is a diagrammatic, perspective view of an embodiment of the invention for forming a unit type strand;

FIG. 2 is a diagrammatic, perspective view of an embodiment of the invention for forming a concentric type strand; and

FIG. 3 is a diagrammatic, perspective view of an embodiment of the invention for forming a unit type strand from a plurality of concentric type strands.

The apparatus illustrated in FIG. 1 is intended to form, for example, a unit type strand, in which each group of conductors is of the concentric type or is in turn divided into groups. Said apparatus defines a path AA, substantially rectilinear, for the continuous passage of the components, in particular, of the groups of the cable, in a direction longitudinally thereof.

In FIG. 1, the tank 1 contains a cable filling medium 2. The medium 2, already heated separately to a temperature higher by at least 5C than its dropping point temperature, is introduced continuously, in a liquid state, through the supply duct 3 and is discharged in a controlled manner through the discharge duct 4, so that the level of the filling medium 2 in the tank 1 remains constant. A preferred filling medium is a petroleum jelly which may be heated to a temperature of about 90C, its dropping point being C.

At the wall 5 of the tank 1, there is a circular plate 6 provided with through holes 7, corresponding in number to the number of the groups of conductors intended to be introduced into the tank 1. A group 8 passes through each hole 7. The groups come from corresponding conventional dies which are situated upstream of the tank 1 and which are not shown in the drawing. As indicated hereinbefore, each of said groups 8 comprises a small number of wires, in order to ensure the complete penetration of the filling medium 2 into the space therebetween.

The level of the filling medium 2 in the tank 1 is such that the plate 6 is completely below said level. Inside the tank 1 and completely immersed in the filling medium 2, there is a die 9 in which the groups 8 are brought together and stranded in a unit type formation. If the stranding of the groups 8 is carried out by means of a conventional rotating paying-off system, the plate 6 may be mounted to rotate about its own axis by means of a revolving shaft (not shown) connected to it and external to the tank 1.

The strand 10 formed by said groups 8 continues to travel in the liquid filling medium 2 and penetrates, through a hole 11 of a wall 12 of the tank 1, and then, travels in a tube 13 which is maintained at a temperature 15C lower than the dropping point temperature of the filling medium 2, the tube 13 being situated, for example, in a container 14 in which a liquid circulates at said lower temperature. The tube 13 has its free end 15 opening at the outside of the container 14.

Connected to the wall 5 of the tank 1, there is a container 16 for collecting the filling medium 2 which flows out from the holes 7 of the plate 6. Said container 16, provided with a discharge duct 17 for discharging the excess of the filling medium 2, is maintained heated, like thetank 1, so that the filling medium 2 may remain in the liquid state. From the discharge duct 17 the excess of the filling medium 2 can be conveyed and recirculated to the tank 1 through the duct 3 of the latter, by means of conventional recirculating means.

For the sake of simplicity, the drawing does not illustrate a heat exchanger able to maintain the filling medium 2 in the tank 1 at the pre-established temperature, the heating means for the collecting container 16 or the heater exchanger able to maintain the tube 13 at the desired temperature. However, each of these is wellknown to those skilled in the art.

, The tank 1 has relatively small dimensions. To carry out the filling of the groups 8 with the filling medium 2 as described hereinbefore, it is in fact sufficient for the tank 1 to have a length of the order of 50 centimeters and a height of the order of 20 centimeters. Said dimensions, however, are mainly dependent on the geometrical configuration of the manufacturing line and on the line speed. i

Each group 8, introduced in the tank 1 through the corresponding hole 7 of the circular plate 6, comes separately into contact with the filling medium 2 contained in liquid state in the tank 1, so that a total impregnation of each group 8 is obtained at the same time and before they are brought together and stranded in the die 9 situated inside the tank 1. As it leaves the die 9, the resulting strand 10 still remains in contact with the filling medium 2 along the zone extendingfrom the die 9 to the wall 12 of the tank 1 provided with the outlet hole 11,.

Although it is not strictly necessary for said zone to be wide, since the complete external covering of the strand can be obtained by a minimum travel of the latter in contact with the liquid filling medium 2, it is preferable for said travel to correspond to about one half of the tank length, so as to ensure, at the minimum, the presence of the filling medium 2 outside the strand 10 being formed. Therefore, the die 9 is generally situated in the middle of the tank 1.

The strand 10 in contact with the liquid filling medium 2 travels along the remaining part of the tank 1 and leaves the tank 1 through the hole 11 of the wall 12, to enter the tube 13. The hole 11 is coaxial with the outlet hole of the die 9, and has a diameter approximately equal to that of the strand 10, and in practice exceeds the diameter of the strand 10 by 2 millimeters at the most. The tube 13 has an inner diameter of similar dimensions.

The passage of the strand 10 in the tube 13, practically in contact with the tube walls, which are at a temperature 15C lower than the dropping point temperature of the filling medium 2, causes a reduction in temperature of the medium 2, with a subsequent rapid change from the liquid to thesemi-solid state. The

length of the tube 13 corresponds approximately to that of the tank 1, so that the strand 10 as it leaves the tube 13 through the free end 15, is filled with a totally semi-solid medium, without any leakage of the filling medium 2 from the strand 10. Moreover, during said passage, the strand 10 is uniformly covered at all points with the filling medium 2, so that, as it leaves the tube 13, the outer layer of filling medium 2 is smoothed and sized and completely surrounds'the outer surface of the strand 10.

As a final result, the strand 10 is completely impregnated with the filling medium 2 both inside and outside, and is ready for the subsequent conventional processing steps for the manufacture of the finished telecommunication cable, e.g., covering the strand 10 with metallic screening tapes and/or'a plastic sheath and if desired, a metal sheath or armor.

The apparatus illustrated in FIG. 2 is particularly intended to form a strand of the concentric type while, at the same time, completely filling it with the filling medium. Said apparatus, like the previously described embodiment, defines a substantially rectilinear path B-B' for the continuous passage of the components in a direction longitudinally thereof and comprises a temperature regulated tank 18, containing the filling medium 2, at a temperature higher by at least 5C than its dropping point temperature. Said tank 18 is provided with a circular plate 19 at one of its walls and with two circular plates 20 and 21 inside the tank 18. All the plates 19-21 are situated below the level of the filling medium 2. Inside the tank 18 there are three dies 22, 23 and 24. The first two dies 22 and 23 are located at the plates 20 and 21, respectively, whereas the third die 24 is located downstream of the plate 21. The strand components 25 which are introduced in the tank 18 consist of single wires or of pairs, quads or trefoils, and

, 22-24 by means of a conventional rotating collection system (not shown) located downstream of the whole filling apparatus.

Specifically, some of the components 25 introduced into the tank 18 are brought together in the die 22 to form subsequently the central layer of the strand 25a. In the meantime, the other components 25 pass instead directly from the holes 19a of the plate 19 through the holes 20a of the plate 20. In turn, some of them are subsequently brought together in the die 23 to form a layer situated on the central layer, while the remaining components pass directly from the holes 20a of the plate 20 to the.- holes 21a of the plate 21 and are subsequently brought together in the die 24 to form the last layer of the strand 25a. Therefore, the strand 25a has three concentric layers of said components 25, which are completely filled with the filling medium 2.

As described in connection with the tank 1, the di- =mensions of the tank 18 depend on the geometrical configuration of the manufacturing line; and on the speed of, the latter. t Analogous to what was described. in respect to the embodimentin FIG. 1, the, strand 25a so formed,.con-

tinuing its longitudinal travel, exits from the tank 18 1 I Therefore, in this embodiment also, the strand 25a in its passagethrough the tube 27 is uniformly covered with the filling'medium 2 now in semi-solid state so that, as it leaves the end 29 of the tube 27, said strand 25a has its outer layer of the filling medium 2 smoothed and sized. Also, the strand 25a is completely filled interiorly thereof.

Connected to the tank 18, there is a heated container 30, like the container 16, for the collection of the filling medium 2 which flows out from the holes 19a of the plate 19. Said container 30 has a discharge duct 31 for discharging the excess of the filling medium 2. The latter canbe returned to the tank 18 as previously indicatedwith reference to the embodiment in FIG. 1. FIG. 2 does not illustrate the heat exchanger able to maintain the filling medium 2 in the tank 18 at the desired temperature, the heating means for the collecting container 30, and the heat exchanger able to maintain the tube 27'at the desired temperature. 1

The apparatus illustrated in FIG. 3 is intended to form a unit type strand, where each group is of concentric type and comprises a great number of wires, and to impregnate, at the same time, said strand with the filling medium. The apparatus comprises three temperature regulated tanks 32, 33 and 34 arranged in parallel, each of which is identical to the previously described tank 18. The components which enter each tank 32, 33 and 34 through the holes of the respective circulate plates 42, 43 or 44, situated at the tank wall, are stranded in said tank to form a concentric group. Said components 25, consisting of individually insulated wires, or of pairs, quads or trefoils of said wires, come from conventional paying-off drums (not shown) situated upstream of each tank. The groups 25 enter the respective tank, and are brought together and stranded in subsequent phases in three dies totally immersed in the liquid filling medium so that, at each outlet 35, 36 and 37, respectively, of the cooling tubes connected to said tanks, there is a group constituted by a central core and two concentric layers of components, which is completely filled with the filling medium in semi-solid state and carries on its outer surface a smoothed and sized layer of said medium. Said groups, in turn, are conveyed and caused to pass through a temperature regulated tank 38 identical to the previously described tanks 32, 33 and 34. In the tank 38, the concentric groups, while they are immersed in the liquid filling medium, are brought together and stranded in a die 39 in a unit type formation. The resulting strand 45 subsequently passes through the cooling tube 40, and therefore, it leaves the free end 41 of said tube 40 completely filled with the filling medium in semi-solid state, carrying on its outer surface a smoothed and sized layer of said filling medium.

In addition to the hereinbefore indicated means for paying off the components, the apparatus is also provided with rotating collection means situated downstream of the filling apparatus 38-41, which imparts the stranding twist both to the groups and to the strand Although preferred embodiments of the present invention have been'described and illustrated, it will be understood by those skilled in the art that various modifications may be made without departing from the principles of the invention.

' i What is claimed is:

1. In a process for manufacturing a fully-filled cable comprising a plurality of conductive components of elongated shape surrounded by at least a waterimpermeable sheath and twisted into a strand, the spaces within said sheath and between the components being filled with a water-impermeable and electrically insulating filling medium having a predetermined dropping point temperature, the method of filling and coating said components which comprises feeding said components longitudinally along a predetermined path while twisting them to form said strand at a predetermined position along said path spaced from the beginning thereof, immersing each of said components in said filling medium at a temperature above said dropping point temperature in advance of said position so that said components are each individually immersed in said bath prior to the position at which said strand has been formed, maintaining both said components and said strand immersed in said filling medium at said temperature as said components are twisted in advance of said position and as said strand is formed at said position and as the strand is fed beyond said position, cooling the filling medium on said strand to a temperature below said dropping temperature, to thereby solidify said medium, and smoothing the peripheral surface of the medium on said strand.

2. A process asset forth in claim 1, wherein'the filling medium in which said components are'immersed during twisting is'maintained at a temperature at least 5C above said dropping point temperature and said medium on said strand is cooled to a temperature at least 5C below said dropping point temperature.

3. A process as set forth'in claim 2, wherein said strand is maintained immersed in said mediumat said temperature 5C above said dropping point temperature as it is fed beyond said position and until it reaches a further position at which said medium on said strand is simultaneously cooled and smoothed to a predetermined size.

4. Apparatus for cooling and filling the spaces within a strand of elongated conductive componentswith a water-impermeable and electrically insulating filling medium having a predetermined dropping point temperature during the twisting of the components forming said strand comprising at least one temperature regulated tank for receiving said filling medium and maintaining said medium at a temperature above said dropping point temperature and at a predetermined level, said tank having a first wall at one end of said tank and a second wall at the opposite end of said tank, said first wall having a plate portion with a plurality of holes therethrough, one for each of saidcomponents, disposed in spaced relation to each other around the center of a circle, said holes being located below said level of said medium, said second wall having a hole therethrough approximately equal but greater insize than the periphery of said strand and said hole being located below said level'of said medium, at least one stranding die in said tank between said plate and said-hole for receiving said components and guiding them as they are stranded at said die, said die being located below. said level of said medium, a tube connected at one end to said hole and located exteriorly of said tank for receiving and guiding said strand as it leaves said tank, said tube having an internal size approximately. equal to but greater in size than the periphery of said strand for smoothing and shaping the medium on said strand, and means for cooling said tube to a temperature below said dropping point temperature.

5. Apparatus as set forth, in claim .4, wherein said size of said tube is greater than said size of said strand 'by a maximum of two millimeters. a

6. Apparatus as set forth in claim 4,.wherein said plate portion is mounted for rotation around an axis at said center of said circle. I

7. Apparatus as set forth in claim 4, further comprising a container at said first wall and exterior to said tank for receiving such portion of said medium which flows out of said tank through said holes in said plate portion, and means for discharging said portion from said container. 

1. In a process for manufacturing a fully-filled cable comprising a plurality of conductive components of elongated shape surrounded by at least a water-impermeable sheath and twisted into a strand, the spaces within said sheath and between the components being filled with a water-impermeable and electrically insulating filling medium having a predetermined dropping point temperature, the method of filling and coating said components which comprises feeding said components longitudinally along a predetermined path while twisting them to form said strand at a predetermined position along said path spaced from the beginning thereof, immersing each of said components in said filling medium at a temperature above said dropping point temperature in advance of said position so that said components are each individually immersed in said bath prior to the position at which said strand has been formed, maintaining both said components and said strand immersed in said filling medium at said temperature as said components are twisted in advance of said position and as said strand is formed at said position and as the strand is fed beyond said position, cooling the filling medium on said strand to a temperature below said dropping temperature, to thereby solidify said medium, and smoothing the peripheral surface of the medium on said strand.
 2. A process as set forth in claim 1, wherein the filling medium in which said components are immersed during twisting is maintained at a temperature at least 5C above said dropping point temperature and said medium on said strand is cooled to a temperature at least 5*C below said dropping point temperature.
 3. A process as set forth in claim 2, wherein said strand is maintained immersed in said medium at said temperature 5*C above said dropping point temperature as it is fed beyond said position and until it reaches a further position at which said medium on said strand is simultaneously cooled and smoothed to a predetermined size.
 4. Apparatus for cooling and filling the spaces within a strand of elongated conductive components with a water-impermeable and electrically insulating filling medium having a predetermined dropping point temperature during the twisting of the components forming said strand comprising at least one temperature regulated tank for receiving said filling medium and maintaining said medium at a temperature above said dropping point temperature and at a predetermined level, said tank having a first wall at one end of said tank and a second wall at the opposite end of said tank, said first wall having a plate portion with a plurality of holes therethrough, one for each of said components, disposed in spaced relation to each other around the center of a circle, said holes being located below said level of said medium, said second wall having a hole therethrough approximately equal but greater in size than the periphery of said strand and said hole being located below said level of said medium, at least one stranding die in said tank between said plate and said hole for receiving said components and guiding them as they are stranded at said die, said die being located below said level of said medium, a tube connected at one end to said hole and located exteriorly of said tank for receiving and guiding said strand as it leaves said tank, said tube having an internal size approximately equal tO but greater in size than the periphery of said strand for smoothing and shaping the medium on said strand, and means for cooling said tube to a temperature below said dropping point temperature.
 5. Apparatus as set forth in claim 4, wherein said size of said tube is greater than said size of said strand by a maximum of two millimeters.
 6. Apparatus as set forth in claim 4, wherein said plate portion is mounted for rotation around an axis at said center of said circle.
 7. Apparatus as set forth in claim 4, further comprising a container at said first wall and exterior to said tank for receiving such portion of said medium which flows out of said tank through said holes in said plate portion, and means for discharging said portion from said container. 